Near eye display with intermediate window

ABSTRACT

A near eye display including: a first optical waveguide having a direction of elongation, at least one pair of parallel faces, and a first coupling-out mechanism; a second optical waveguide having an input aperture, a pair of parallel faces, and a second coupling out-mechanism; an optical coupling between the first optical waveguide and the second waveguide, the optical coupling including at least an air gap configured to enable total internal reflection within the first waveguide, and an interface window, the interface window comprising a transparent optical element with a refractive index substantially the same as a refractive index of the second optical waveguide; and wherein at least a portion of the interface window projects beyond the input aperture of the second optical waveguide such that undesired light exiting the first waveguide is prevented from entering the second waveguide.

TECHNICAL FIELD

The presently disclosed subject matter relates to a near eye display,and, more particularly, to a near eye display with an intermediateinterface window.

BACKGROUND

Certain near eye displays and head up displays having 2D expansion ofthe aperture include two waveguide (or “light guide”) sections. Thefirst section expands the aperture in one dimension and the secondexpands in the orthogonal dimension. A first example is described inU.S. Pat. No. 7,643,214 which employs waveguides which are based on asingle pair of parallel surfaces for expansion in each dimension. Afurther set of examples are shown in FIGS. 22A-22B of PCT/IL2017/051028,(reproduced herein as FIG. 2), where the waveguide of a first dimensionof aperture expansion has two mutually orthogonal pairs of parallelsurfaces which guides image light through four-fold internal reflection.This figure describes various interface configurations between the twowaveguides.

In order to maintain total internal reflection within the firstwaveguide, some of these configurations are based on an air-gap betweenthe waveguides that need to be sealed. Throughout the remainder of thisdocument, the term “air-gap” is used to refer to air or any othermaterial with a sufficiently low refractive index to preserve TIR withinwaveguide 10 for a range of angles of image illumination correspondingto an image field of view.

Both waveguides have to be mechanically combined and held firmly infront of the viewer. Furthermore, the interface between the waveguidespreferably has a well-defined aperture which performed trimming in orderto achieve generally uniform illumination along the waveguide.

GENERAL DESCRIPTION

According to one aspect of the presently disclosed subject matter thereis provided a near eye display including: a first optical waveguidehaving a direction of elongation, at least one pair of parallel faces,and a first coupling-out mechanism; a second optical waveguide having aninput aperture having a pair of parallel faces, and a second couplingout-mechanism; an optical coupling between the first optical waveguideand the second waveguide, the optical coupling including at least an airgap configured to enable total internal reflection within the firstwaveguide and an interface window, the interface window including atransparent optical element with a refractive index substantially thesame as a refractive index of the second optical waveguide; and at leastone light absorbent element; wherein at least a portion of the interfacewindow projects beyond the input aperture of the second opticalwaveguide and serves as a structural support for the at least one lightabsorbent element.

According to another aspect of the presently disclosed subject matterthere is provided a near eye display including: a first opticalwaveguide having a direction of elongation, at least one pair ofparallel faces, and a first coupling-out mechanism; a second opticalwaveguide having an input aperture, a pair of parallel faces, and asecond coupling out-mechanism; an optical coupling between the firstoptical waveguide and the second waveguide, the optical couplingincluding at least an air gap configured to enable total internalreflection within the first waveguide, and an interface window, theinterface window including a transparent optical element with arefractive index substantially the same as a refractive index of thesecond optical waveguide; and wherein at least a portion of theinterface window projects beyond the input aperture of the secondoptical waveguide such that undesired light exiting the first waveguideis prevented from entering the second waveguide.

According to some aspects, the at least one light absorbent elementextends over a portion of the second optical waveguide, preferably in adirection parallel to the third pair of parallel faces.

According to some aspects, the at least one light absorbent elementincludes a baffle.

According to some aspects, the at least one light absorbent elementencapsulates the first optical waveguide. Preferably the at least onelight absorbent element includes a cover. Preferably the coverencapsulates the first optical waveguide such that an air gap remainsbetween the faces of the first optical waveguide and the cover.Preferably the cover is configured to prevent ingress of dirt andhumidity into the air gap.

According to some aspects, the at least one light absorbent elementincludes each of a cover encapsulating the first optical waveguide, anda baffle extending over a portion of the second optical waveguide.

According to some aspects, the interface window is thicker at one end.Preferably, the interface window is coated with a light absorbentcoating at one or both ends.

According to some aspects, the second optical waveguide is coated with areflective coating at a trimming point of the second optical waveguide.

According to some aspects, the first coupling-out mechanism includes aplurality of internal partially reflecting surfaces at least partiallytraversing the first optical waveguide at an oblique angle to thedirection of elongation, or one or more diffractive elements.

According to some aspects, the second coupling-out mechanism includes aplurality of partially reflecting surfaces at least partially traversingthe second optical waveguide at an oblique angle to the pair of parallelfaces of the second optical waveguide, or one or more diffractiveelements.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it can be carriedout in practice, embodiments will be described, by way of non-limitingexamples, with reference to the accompanying drawings, in which:

FIGS. 1A-1B illustrate a generalized optical aperture multiplieraccording to the prior art;

FIG. 2 illustrates a particular embodiment of an optical aperturemultiplier according to the prior art;

FIGS. 3A-3B illustrate schematic diagrams of a near eye displayaccording to the prior art;

FIGS. 4A-4B illustrate generalized schematic diagrams of a near eyedisplay according to a first embodiment of the present invention;

FIG. 4C illustrates a generalized schematic diagram of a near eyedisplay according to a second embodiment of the present invention;

FIG. 5 illustrates a generalized schematic diagram of a near eye displayaccording to a third embodiment of the present invention; and

FIG. 6 illustrates a generalized schematic diagram of a near eye displayaccording to a fourth embodiment of the present invention.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresently disclosed subject matter may be practiced without thesespecific details. In other instances, well-known methods, procedures,and components have not been described in detail so as not to obscurethe presently disclosed subject matter.

The term “near eye display” as used throughout the description should beunderstood to include other forms of displays that require imageexpansion, including for example heads up displays.

PCT/IL2017/051028, incorporated by reference herein, describes variousembodiments of an optical aperture multiplier, shown generally in FIGS.1A-1B. The optical aperture multiplier includes a first opticalwaveguide 10 having a direction of elongation illustrated arbitrarilyherein as corresponding to the “x-axis”. First optical waveguide 10 hasfirst and second pairs of parallel faces 12 a, 12 b, 14 a, 14 b forminga rectangular cross-section. According to certain particularly preferredembodiments of the present invention, a plurality of internal partiallyreflecting surfaces 40, referred to herein as “facets”, at leastpartially traverse first optical waveguide 10 at an oblique angle (i.e.,neither parallel nor perpendicular) to the direction of elongation.

The optical aperture multiplier preferably also includes a secondoptical waveguide 20, optically coupled with first optical waveguide 10,having a third pair of parallel faces 22 a, 22 b forming a slab-typewaveguide, i.e., where the other two dimensions of waveguide 20 are atleast an order of magnitude greater than the distance between third pairof parallel faces 22 a, 22 b. Here too, a plurality of partiallyreflecting surfaces 45 preferably at least partially traverse secondoptical waveguide 20 at an oblique angle to the third pair of parallelfaces.

The optical coupling between the waveguides, and the deployment andconfiguration of partially reflecting surfaces 40, 45 are such that,when an image is coupled into first optical waveguide 10 with an initialdirection 30 of propagation at a coupling angle oblique to both thefirst and second pairs of parallel faces 12 a, 12 b, 14 a, 14 b, theimage advances by four-fold internal reflection (images a1, a2, a3 anda4) along first optical waveguide 10, with a proportion of intensity ofthe image reflected at partially reflecting surfaces 40 so as to becoupled into second optical waveguide 20, and then propagates throughtwo-fold reflection (images b1, b2) within second optical waveguide 20,with a proportion of intensity of the image reflected at partiallyreflecting surfaces 45 so as to be directed outwards from one of theparallel faces as a visible image c, seen by the eye of a user 47.

PCT/IL2017/051028 further describes a particular embodiment of theoptical aperture multiplier in which the waveguide 10 is inclined withrespect to waveguide 20, as shown in FIG. 2. First waveguide 10 may bemounted at a required inclination relative to ID waveguide 20 by use ofan intermediate transparent wedge 730. This inclination is chosen so asto couple one image from waveguide 10 (solid arrow) and not to couplethe other image from waveguide 10 (dashed arrow). The inclination ofwaveguide 10 relative to waveguide 20 can be chosen according to therequired angles of the waveguides and the images propagating betweenthem, and may employ a transparent wedge coupling prism 730 to eitherdecrease the inclination relative to an inclined coupling surface ofsecond waveguide 20. Alternatively, the required inclination angle offirst waveguide 10 relative to second waveguide 20 matches the angle ofthe second waveguide coupling surface, so that no intermediate couplingprism is needed.

However, in the prior art configurations, in some cases light can bereflected back into waveguide 10 causing image degradation, as shown inFIGS. 3A-3B illustrating a generalized schematic diagram of a near eyedisplay according to the prior art. In FIG. 3A, light is coupled out ofa first waveguide 10, for example a 2D waveguide, through an air gap,through prism 15 and into the second waveguide 20, for example a 1Dwaveguide. Trimming point 21 of waveguide 20 serves as the aperture thattrims unrequired light (typically positioned at a corner of waveguide20). That is, any light rays hitting a point to the right of point 21will reflect out of waveguide 20.

As illustrated in FIG. 3A, parallel light rays 22 a, 22 b and 22 crepresent a single point in the transmitted FOV of an image collimatedto infinity. Ray 22 a enters waveguide 20 near trimming point 21 andpropagates through waveguide 20 via TIR. Ray 22 b reflects off of theface 22 b of waveguide 20 and is reflected back at a point to the leftof point 21 and continues propagating through waveguide 20 via TIR.However, ray 22 c also reflected off of face 22 b hits a point to theright of point 21 and therefore exits the waveguide 20 via the prism 15.

FIG. 3B illustrates an alternative prior art configuration of a near eyedisplay in which the angular design of the waveguides dictates no“wedge” prism between waveguides 10 and 20. In this case, ray 22 c canimpinge on the air-gap face at a shallow angle and consequently reflectback into waveguide 20 as undesired light. This undesired light cancause image degradation.

It should be noted that although FIGS. 3A-3B show waveguide 10 as a 2Dwaveguide with two pairs of parallel faces, the problem of undesiredlight entering waveguide 20 is equally applicable when waveguide 10 is a1D waveguide with one pair of parallel faces, such as the waveguidesdescribed in U.S. Pat. No. 7,643,214 (see particularly, e.g. FIGS.10-15, 17, 18 and 20) which is incorporated by reference herein.

Turning now to the present invention, a near eye display is providedthat improves upon the near eye displays of the prior art. FIGS. 4A-4Billustrate a generalized schematic diagram of a near eye displayaccording to certain embodiments of the presently disclosed subjectmatter. According to one embodiment of the present invention, the neareye display includes a first optical waveguide 10, a second opticalwaveguide 20, and an optical coupling between waveguide 10 and waveguide20 consisting of an air gap 29 and an intermediate interface window 30.

As in the prior art, waveguide 10 has a direction of elongation, atleast one pair of parallel faces 12 a, 12 b, and a coupling-outmechanism 40. In some embodiments, waveguide 10 can have two pairs ofparallel faces 12 a, 12 b, 14 a, 14 b. In some embodiments, and as shownin FIG. 1B, the coupling-out mechanism 40 can be, for example, aplurality of internal partially reflecting surfaces that at leastpartially traverse waveguide 10 at an oblique angle to the direction ofelongation. In other embodiments, the coupling-out mechanism can be, forexample, one or more diffractive elements. In some embodiments, thefaces of waveguide 10 other than the output surface may be coated withreflective coatings.

Also as in the prior art, waveguide 20 has a pair of parallel faces 22a, 22 b, and a coupling-out mechanism 45, such as a plurality ofpartially reflecting surfaces that at least partially traverse waveguide20 at an oblique angle to the pair of parallel faces, or one or morediffractive elements. Preferably, waveguide 10 is slightly wider thanwaveguide 20.

As detailed above, the optical coupling between waveguides 10 and 20includes an air gap 29 and an interface window 30. The interface windowis preferably made from a transparent optical element with a refractiveindex substantially the same as a refractive index of the waveguide 20.By “substantially the same” refractive index it is meant that light raysshould be able to pass through the border between interface 30 andwaveguide 20 substantially intact, i.e. without redirection.

The interface window 30 preferably overlaps the entire input aperture ofthe second waveguide 20, and in certain preferred cases projects beyondthat aperture as shown in FIGS. 4A-4B, thereby enabling ray 22 c toreflect out of the near eye display without entering waveguide 20. Inaddition, as will be detailed below with reference to FIGS. 5-6, incertain preferred embodiments the portion(s) of the interface windowthat project beyond the input aperture of waveguide 20 can additionallyserve as structural support for additional components of the near eyedisplay.

The minimal thickness of interface window 30 should be set so no TIRthat is generated in the window side of the air-gap in the entiretransmitted image field will be able to return to waveguide 20 and willexit through the side of window 30. Maximally, the thickness of thewindow is preferably less than a thickness of the waveguide 20 itself asmeasured between the major parallel faces of the waveguide. A small airgap preferably preserves TIR conditions for light propagating within thefirst waveguide 10. The gap may advantageously be maintained by mountingthe first waveguide 10 via its end surfaces, i.e., the dimension “intothe page” of the drawings as illustrated, via any suitable supportstructure and adhesive.

According to another embodiment of the present invention, the interfacewindow 30 may be thicker at one end, as shown in FIG. 4B. For example,this may be necessary in cases where the design of the near eye displaycalls for a small angle between waveguide 10 and waveguide 20.

FIG. 4C illustrates another embodiment of a near eye display including afirst 1D waveguide 1000, a second optical waveguide 20, and an opticalcoupling between waveguide 1000 and waveguide 20 consisting of an airgap 29 and an intermediate interface window 30. In this embodiment,waveguide 1000 is a 1D waveguide with one pair of parallel faces 12 a,12 b for propagating light rays via TIR, such as the waveguidesdisclosed in U.S. Pat. No. 7,643,214 (in particular the embodimentsshown in FIGS. 10-15, 17, 18 and 20). Similar to waveguide 10, waveguide1000 has a direction of elongation and a coupling-out mechanism, whichcan be, for example, a plurality of internal partially reflectingsurfaces that at least partially traverse waveguide 1000 at an obliqueangle to the direction of elongation, or one or more diffractiveelements.

Preferably, in this case, the ends of the waveguide 1000 (i.e. the facesperpendicular to the pair of parallel faces 21, 12 b) are coated with alight absorbent coating 1002, or at least an outward transmissivecoating, in order to prevent outside light from entering the waveguide.Preferably, interface window is also coated at its ends with coating1002.

Another embodiment of the present invention is shown in FIG. 5, in whichthe interface window 30 is also used a base for securing one or moreadditional components to the near eye display. In this embodiment, thenear eye display includes at least one light absorbent element such ascover 35 and/or baffle 36 which is secured to the interface window 30and provides additional advantages over the near eye displays of theprior art, as will be further detailed below. It should be noted thatwhile FIG. 5 shows a near eye display having both cover 35 and baffle36, the near eye display can in fact include only the cover 35, only thebaffle 36, or both cover 35 and baffle 36.

Baffle 36 is configured to prevent scattered light from radiatingoutward and preventing ambient light from being coupled in. The baffle36 preferably extends over a portion of waveguide 20, and mostpreferably in a direction parallel to parallel faces 22 a, 22 b.

Cover 35 encapsulates waveguide 10 while preferably leaving an air gapbetween the cover and the faces of waveguide 10 in order to maintain TIRconditions. This cover prevents ambient light from passing throughwaveguide 10 onto waveguide 20 thereby causing image degradation.Preferably the cover is configured to also prevent ingress of dirt andhumidity into the air-gap which would interfere with image transmission.

As detailed above, the near eye display of the present invention can insome cases include both a cover 35 and a baffle 36, in which case bothelements are collectively referred to as light absorbent elements forthe purposes of this description.

The end portions 34 a, 34 b of the interface window 30 are not used foroptical transmittance or for reflectance (TIR) and can therefore be usedto secure the light absorbent element(s) such as encapsulating cover 35and/or baffle 36.

Preferably, the window 30 is coated at its end faces with a lightabsorbent coating 37 to further improve image transmittance.

In some embodiments, in order to improve the optical quality of thetrimming point 21, a reflective coating 39 can be applied on a face ofwaveguide 20 at trimming point 21 as described in PCT patent publicationno. WO 2018/087756.

Another embodiment of the present invention is shown in FIG. 6, in whichthe interface window is not inclined with respect to waveguide 20 and/orwave guide 10 and is used solely a base for securing additionalcomponents to the near eye display, such as cover 35 and/or baffle 36.

It is to be understood that the invention is not limited in itsapplication to the details set forth in the description contained hereinor illustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Hence, it is to be understood that the phraseology and terminologyemployed herein are for the purpose of description and should not beregarded as limiting. As such, those skilled in the art will appreciatethat the conception upon which this disclosure is based may readily beutilized as a basis for designing other structures, methods, and systemsfor carrying out the several purposes of the presently disclosed subjectmatter.

1. A near eye display comprising: a first optical waveguide having adirection of elongation, at least one pair of parallel faces, and afirst coupling-out mechanism; a second optical waveguide having an inputaperture having a pair of parallel faces, and a second couplingout-mechanism; an optical coupling between said first optical waveguideand said second waveguide, said optical coupling including at least anair gap configured to enable total internal reflection within the firstwaveguide and an interface window, the interface window comprising atransparent optical element with a refractive index substantially thesame as a refractive index of said second optical waveguide; and atleast one light absorbent element; wherein at least a portion of saidinterface window projects beyond the input aperture of said secondoptical waveguide and serves as a structural support for said at leastone light absorbent element.
 2. The near eye display of claim 1, whereinthe at least one light absorbent element extends over a portion of saidsecond optical waveguide.
 3. The near eye display of claim 2, whereinthe at least one light absorbent element extends over a portion of thesecond optical waveguide in a direction parallel to the third pair ofparallel faces.
 4. The near eye display of claim 2, wherein the at leastone light absorbent element comprises a baffle.
 5. The near eye displayof claim 1, wherein the at least one light absorbent elementencapsulates said first optical waveguide.
 6. The near eye display ofclaim 5, wherein the at least one light absorbent element comprises acover.
 7. The near eye display of claim 6, wherein the coverencapsulates said first optical waveguide such that an air gap remainsbetween the faces of said first optical waveguide and said cover.
 8. Thenear eye display of claim 7, wherein the cover is configured to preventingress of dirt and humidity into the air gap.
 9. The near eye displayof claim 1, wherein said at least one light absorbent element compriseseach of a cover encapsulating said first optical waveguide, and a baffleextending over a portion of said second optical waveguide.
 10. The neareye display of claim 1, wherein the interface window is thicker at oneend.
 11. The near eye display of claim 1, wherein the interface windowis coated with a light absorbent coating at one or both ends.
 12. Thenear eye display of claim 1, wherein said second optical waveguide iscoated with a reflective coating at a trimming point of said secondoptical waveguide.
 13. The near eye display of claim 1, wherein thefirst coupling-out mechanism comprises a plurality of internal partiallyreflecting surfaces at least partially traversing the first opticalwaveguide at an oblique angle to the direction of elongation.
 14. Thenear eye display of claim 1, wherein the first coupling-out mechanismcomprises one or more diffractive elements.
 15. The near eye display ofclaim 1, wherein the second coupling-out mechanism comprises a pluralityof partially reflecting surfaces at least partially traversing thesecond optical waveguide at an oblique angle to the pair of parallelfaces of the second optical waveguide.
 16. The near eye display of claim1, wherein the second coupling-out mechanism comprises one or morediffractive elements.
 17. A near eye display comprising: a first opticalwaveguide having a direction of elongation, at least one pair ofparallel faces, and a first coupling-out mechanism; a second opticalwaveguide having an input aperture, a pair of parallel faces, and asecond coupling out-mechanism; an optical coupling between said firstoptical waveguide and said second waveguide, said optical couplingincluding at least an air gap configured to enable total internalreflection within the first waveguide, and an interface window, theinterface window comprising a transparent optical element with arefractive index substantially the same as a refractive index of saidsecond optical waveguide; and wherein at least a portion of saidinterface window projects beyond the input aperture of said secondoptical waveguide such that undesired light exiting the first waveguideis prevented from entering the second waveguide.